CN112748308B - Micro-grid single-end rapid fault positioning method and related device - Google Patents
Micro-grid single-end rapid fault positioning method and related device Download PDFInfo
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Abstract
The application discloses a method and a related device for rapidly positioning a single-end fault of a micro-grid, which judge whether a fault occurs or not through the output voltage of a micro-grid inverter or the three-phase grid-incoming current; when the micro-grid fails, the droop control mode of the inverter is switched to a current control mode, so that fault ride-through is realized; then constructing a fault loop differential equation of the protected line with the fault; then, different times of harmonic waves are respectively superposed on the modulation waves of the micro-grid, and a plurality of high-frequency harmonic waves with different frequencies are injected into the micro-grid, so that the micro-grid filters the harmonic voltage of the protected line with the fault through the high-frequency harmonic waves to obtain a high-frequency signal; finally, fault distance calculation is carried out by adopting high-frequency signals in the power grid; the method can complete the quick, accurate and reliable judgment and positioning of the faults of the micro-grid system under the condition of no communication, thereby solving the technical problems of low positioning accuracy, long time and unreliability of the existing micro-grid fault positioning technology.
Description
Technical Field
The application relates to the technical field of electric power, in particular to a method and a related device for rapidly positioning a single-ended fault of a micro-grid.
Background
The micro-grid is used as a small power generation and distribution system organically integrating a distributed micro-source, a load, an energy storage device and a power electronic converter, can operate in a grid-connected mode or an island mode, and the safe and stable operation capability of the micro-grid is the first guarantee for realizing large-scale application of the micro-grid. However, compared with the characteristics of large power grid, such as large inertia and strong damping, the micro-grid, as a power electronic system, exhibits the operating characteristics of small inertia and weak damping, and when the system fails, the system needs to be rapidly cleared, otherwise, instability easily occurs to cause system breakdown, and thus the requirement of the micro-grid on the rapidity of the relay protection device is very high.
At present, the scheme for protecting the microgrid mainly comprises double-end quantity protection and single-end quantity protection, wherein the double-end quantity protection scheme needs to exchange fault information on two sides of a protected circuit of the microgrid, full-line quick action can be realized based on communication, certain communication delay exists, and when a communication system fails, the fault of the microgrid cannot be judged and positioned; the single-end protection scheme is mainly characterized in that fault current amplitude information and delay action time are matched with each line protection device in a coordination system, and for high-transition resistance faults or line end faults, time required by protection action is longer, so that fault positioning time is overlong; and the microgrid system has short circuit, so that the fault positioning accuracy is low.
Therefore, it is desirable to provide a method and a device for positioning a single-ended fault of a microgrid quickly, accurately and reliably.
Disclosure of Invention
The embodiment of the application provides a method and a related device for rapidly positioning a fault of a single end of a micro-grid, and is used for solving the technical problems of low positioning accuracy, long time and unreliability of the existing micro-grid fault positioning technology.
In view of this, a first aspect of the present application provides a method for locating a single-ended fast fault of a microgrid, where the method includes:
s1, when the output voltage of an inverter of the microgrid is smaller than a preset voltage or the three-phase grid-incoming current of the inverter is larger than a preset current, switching the droop control mode of the inverter into a current control mode;
s2, when phase-to-phase faults occur between the phase A and the phase B of the microgrid, constructing fault loop differential equations of the phase A and the phase B on the m side of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer;
s3, performing reverse park transformation on an inner ring current closed-loop control output value of the inverter type micro source of the microgrid to obtain a three-phase modulation wave, and performing superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers;
s4, respectively injecting N high-frequency harmonics with different frequencies into the microgrid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics;
and S5, substituting the N voltage harmonics and the current harmonics of the m side of the protected line with the phase-to-phase fault into the differential equation of the fault loop, and calculating to obtain the distance between the fault position and the m side.
Optionally, step S2 specifically includes:
when a phase-to-phase fault occurs between the phase A and the phase B of the microgrid, converting the microgrid into an R-L equivalent model, constructing fault loop differential equations of the phase A and the phase B on the side m of the microgrid according to line voltage between the phase A and the phase B on the side m, phase A current on the side m and phase B current, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer.
Optionally, step S5 specifically includes:
substituting N voltage harmonics and current harmonics on the m side of a protected line with phase-to-phase fault into a fault loop differential equation, replacing a differential term of the fault loop differential equation with differential operation, and solving by a least square method to obtain the distance between a fault position and the m side.
Optionally, the three-phase modulated wave is:
in the formula umda、umdb、umdcModulated waves, U, of A, B, C phases respectivelymdFundamental wave amplitude of the output voltage for the inner loop current closed-loop control, omega is the frequency of the output voltage for the inner loop current closed-loop control,
and controlling the phase of the output voltage for the inner loop current in a closed loop mode.
Optionally, the fault loop differential equation is:
in the formula umab(t) is the line voltage between m-side AB phases of the line to be protected, ima、imbRespectively m side A phase current and B phase current of a protected line, r is a resistance per unit length of the line, L is a distance between a fault position and the m side, L is an inductance per unit length of the line, k is a resistance per unit length of the linefAs a branching coefficient into a fault point, RfTransition resistance, R'fEquivalent transition resistance.
This application second aspect provides a little quick fault location device of electric wire netting single-ended, the device includes:
the switching unit is used for switching the droop control mode of the inverter into the current control mode when the output voltage of the inverter of the microgrid is smaller than a preset voltage or the three-phase grid-incoming current of the inverter is larger than a preset current;
the device comprises a construction unit, a fault detection unit and a fault analysis unit, wherein the construction unit is used for constructing fault loop differential equations of an A phase and a B phase at the m side of the microgrid when an interphase fault occurs between the A phase and the B phase of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer;
the modulation unit is used for carrying out reverse park transformation on an inner ring current closed-loop control output value of an inverter type micro source of the micro grid to obtain a three-phase modulation wave, and carrying out superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers;
the injection unit is used for respectively injecting N high-frequency harmonics with different frequencies into the microgrid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics;
and the calculating unit is used for substituting the N voltage harmonics and the current harmonics of the m side of the protected line with the phase-to-phase fault into the differential equation of the fault loop to calculate the distance between the fault position and the m side.
Optionally, the building unit is specifically configured to:
when an interphase fault occurs between the phase A and the phase B of the microgrid, converting the microgrid into an R-L equivalent model, constructing fault loop differential equations of the phase A and the phase B of the microgrid on the side m according to line voltage between the phase A and the phase B on the side m, phase A current on the side m and phase B current, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein the N is a positive integer.
Optionally, the computing unit is specifically configured to:
substituting N voltage harmonics and current harmonics of the m side of the protected line with the phase-to-phase fault into a fault circuit differential equation, replacing a differential term of the fault circuit differential equation with differential operation, and solving by a least square method to obtain the distance between a fault position and the m side.
The third aspect of the present application provides a micro-grid single-ended fast fault location device, where the device includes a processor and a memory:
the memory is used for storing program codes and transmitting the program codes to the processor;
the processor is configured to execute the steps of the method for positioning a single-ended fast fault of a microgrid according to the first aspect.
A fourth aspect of the present application provides a computer-readable storage medium, where the computer-readable storage medium is used to store program codes, and the program codes are used to execute the method for positioning a single-ended fast fault of a microgrid according to the first aspect.
According to the technical scheme, the embodiment of the application has the following advantages:
in an embodiment of the present application, a method for quickly locating a single-ended fault of a micro-grid is provided, including: s1, when the output voltage of the inverter of the microgrid is smaller than a preset voltage or the three-phase grid-incoming current of the inverter is larger than a preset current, switching the droop control mode of the inverter into a current control mode; s2, when phase-to-phase faults occur between the phase A and the phase B of the microgrid, constructing fault loop differential equations of the phase A and the phase B on the m side of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer; s3, performing reverse park transformation on an inner ring current closed-loop control output value of an inverter type micro source of the microgrid to obtain three-phase modulation waves, and performing superposition of X-order harmonic waves and Y-order harmonic waves on the three-phase modulation waves respectively, wherein X and Y are positive integers; s4, respectively injecting N high-frequency harmonics with different frequencies into the micro-grid according to the number N of unknown parameters to respectively obtain N voltage harmonics and N current harmonics; and S5, substituting the N voltage harmonics and the current harmonics of the m side of the protected line with the phase-to-phase fault into a fault loop differential equation, and calculating to obtain the distance between the fault position and the m side.
According to the method for rapidly positioning the fault of the single end of the microgrid, whether the microgrid has a fault or not is judged according to the output voltage or the three-phase grid-incoming current of the inverter of the microgrid; when the micro-grid fails, the droop control mode of the inverter is switched to a current control mode, so that fault ride-through is realized; then constructing a fault loop differential equation of the protected line with the fault; then, different times of harmonic waves are respectively superposed on modulation waves of inner loop current closed-loop control of the micro-grid inversion type micro-source, and a plurality of high-frequency harmonic waves with different frequencies are injected into the micro-grid, so that the micro-grid filters harmonic voltage and the like of a protected line with a fault through the high-frequency harmonic waves to obtain high-frequency signals; finally, the high controllability of the power electronic converter is fully utilized, fault distance calculation is carried out by adopting high-frequency signals in the power grid, and the fault of the micro-grid system can be quickly, accurately and reliably judged and positioned under the condition of no communication, so that the technical problems of low positioning accuracy, long time and unreliability of the conventional micro-grid fault positioning technology are solved.
Drawings
Fig. 1 is a schematic flowchart of a first embodiment of a method for positioning a single-ended fast fault of a micro-grid according to an embodiment of the present application;
fig. 2 is a schematic flowchart of a second embodiment of a method for positioning a single-ended fast fault of a micro-grid according to an embodiment of the present application;
fig. 3 is a structural diagram of an embodiment of a micro-grid single-ended fast fault location apparatus provided in an embodiment of the present application;
FIG. 4 is a diagram of an exemplary microgrid system architecture as provided in an embodiment of the present application;
FIG. 5 is a block diagram illustrating a fault ride-through control of a droop control type IBDG provided in an embodiment of the present application;
fig. 6 is a structural diagram of a fault detection module of the droop control type IBDG provided in the embodiment of the present application;
fig. 7 is an AB phase fault network diagram of a protected line provided in an embodiment of the present application;
fig. 8 is a diagram of a high-frequency harmonic extraction module provided in an embodiment of the present application.
Detailed Description
In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
Referring to fig. 1, a first embodiment of a method for positioning a single-ended fast fault of a micro-grid provided in an embodiment of the present application includes:
It should be noted that, when a fault occurs in a microgrid, a fault detection unit of an inverter type micro source (IBDG) of the microgrid comprehensively determines a change condition of an output voltage and a phase-to-grid current of the inverter, triggers a corresponding protection setting value (a preset voltage and a threshold current), and then generates a grid fault signal, and a control system module of the inverter of the IBDG switches a droop control mode into a current control mode to implement fault ride-through.
102, when phase-to-phase faults occur between the phase A and the phase B of the microgrid, constructing fault loop differential equations of the phase A and the phase B on the m side of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer.
It should be noted that, because the existing 10kV network is an ungrounded system, interphase short-circuit faults occur more often, and for example, AB interphase short-circuit faults are taken as an example, differential equations of fault loops of a phase a and a phase B on the m side of the microgrid can be listed; it can be understood that, since the high frequency harmonics are required to be injected into the power grid in step 104, and the number of the injected high frequency harmonics is determined by the number of unknown parameters of the fault loop differential equation, for example, the fault distance and the equivalent transition resistance are unknown parameters, the number of the unknown parameters is two.
And 103, performing inverse park transformation on the inner ring current closed-loop control output value of the inverter type micro source of the micro grid to obtain a three-phase modulation wave, and performing superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers.
It should be noted that, in the present embodiment, after a three-phase modulation wave is obtained by performing inverse park transformation on an inner loop current closed-loop control output value to obtain a three-phase modulation wave, 8 th harmonics and 10 th harmonics are superimposed on the three-phase modulation wave.
And 104, injecting N high-frequency harmonics with different frequencies into the micro-grid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics.
It should be noted that, in this embodiment, the number of unknown parameters is two, which are the fault distance and the equivalent transition resistance, so that two high-frequency harmonics of 400Hz and 500Hz are injected into the microgrid, respectively, so that voltage and current information measured by the m-side protection device of the protected line with the fault of the microgrid is filtered by the band-pass filters with characteristic frequencies of 400Hz and 500Hz, respectively, to obtain m-side 8-order and 10-order voltage and current harmonics.
And 105, substituting the N voltage harmonics and the current harmonics of the m side of the protected line with the phase-to-phase fault into a fault loop differential equation, and calculating to obtain the distance between the fault position and the m side.
It should be noted that 8 th and 10 th harmonics of the voltage and current are substituted into a differential equation of the fault loop to be solved, so as to obtain the distance between the fault location and the m side, thereby accurately positioning the fault. The high controllability of the power electronic converter is fully utilized, and the fault distance is quickly calculated by adopting high-frequency signals in the power grid. And because the positioning method is single-ended quantity protection, the fault can be judged and positioned without communication, and the reliability and timeliness of fault positioning are ensured.
According to the method for rapidly positioning the fault of the single end of the microgrid, whether the microgrid has a fault or not is judged according to the output voltage or the three-phase grid-incoming current of the inverter of the microgrid; when the micro-grid fails, the droop control mode of the inverter is switched to a current control mode, so that fault ride-through is realized; then constructing a fault loop differential equation of the protected line with the fault; then, different times of harmonic waves are respectively superposed on modulation waves of inner loop current closed-loop control of the micro-grid inversion type micro-source, and a plurality of high-frequency harmonic waves with different frequencies are injected into the micro-grid, so that the micro-grid filters harmonic voltage and the like of a protected line with a fault through the high-frequency harmonic waves to obtain high-frequency signals; finally, the high controllability of the power electronic converter is fully utilized, fault distance calculation is carried out by adopting high-frequency signals in the power grid, and the fault of the micro-grid system can be quickly, accurately and reliably judged and positioned under the condition of no communication, so that the technical problems of low positioning accuracy, long time and unreliability of the conventional micro-grid fault positioning technology are solved.
The foregoing is a first embodiment of a method for positioning a single-ended fast fault of a micro-grid provided in an embodiment of the present application, and the following is a second embodiment of the method for positioning a single-ended fast fault of a micro-grid provided in an embodiment of the present application.
Referring to fig. 2, a second embodiment of a method for positioning a single-ended fast fault of a micro-grid according to the present application includes:
Step 201 is the same as step 101 of the first embodiment, please refer to step 101, and will not be described herein again.
It should be noted that, because the micro-grid system has a small scale and a short line length, the line and the system of the micro-grid are converted into an R-L equivalent model in the embodiment of the application; in addition, the existing 10kV network is an ungrounded system, and an interphase short-circuit fault occurs more often, so this embodiment takes an AB interphase short-circuit fault as an example, and a fault loop differential equation of an m-side a-phase and a B-phase of a microgrid is constructed according to a line voltage between the m-side a-phase and the B-phase, an m-side a-phase current and a B-phase current, it can be understood that since a high-frequency harmonic needs to be injected into the microgrid in step 204, and the number of injected high-frequency harmonics is determined by the number of unknown parameters of the fault loop differential equation, for example, a fault distance and an equivalent transition resistance are unknown parameters, the number of the unknown parameters is two.
The differential equation of the fault loop is as follows:
in the formula umab(t) is the line voltage between m-side AB phases of the line to be protected, ima、imbRespectively m-side A-phase current and B-phase current of a protected line, r is a resistance per unit length of the line, L is a distance between a fault position and the m side, L is an inductance per unit length of the line, and k isfAs a branching coefficient into a fault point, RfTransition resistance, R'fEquivalent transition resistance.
And 203, performing inverse park transformation on the inner ring current closed-loop control output value of the inverter type micro source of the micro grid to obtain a three-phase modulation wave, and performing superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers.
Step 203 is the same as the description of step 103 in the first embodiment, please refer to the description of step 103, which is not repeated herein.
Wherein the three-phase modulation wave is as follows:
in the formula umda、umdb、umdcModulated waves, U, of A, B, C phases respectivelymdFundamental wave amplitude of the output voltage is controlled in a closed loop mode for the inner loop current, omega is the frequency of the output voltage controlled in the closed loop mode for the inner loop current,
the phase of the output voltage is closed-loop controlled for the inner loop current.
And 204, injecting N high-frequency harmonics with different frequencies into the micro-grid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics.
In the embodiment, 8-th harmonic and 10-th harmonic are superposed on a three-phase modulation wave, and two high-frequency harmonics of 400Hz and 500Hz are injected into a microgrid system, so that the three-phase modulation wave obtained by modulation through an inverter modulation module is converted into umda1、umdb1、umdc1：
Wherein:
in the formula umda、umdb、umdcModulated waves, U, of A, B, C phases respectivelymdFundamental wave amplitude of the output voltage is controlled in a closed loop mode for the inner loop current, omega is the frequency of the output voltage controlled in the closed loop mode for the inner loop current,
and controlling the phase of the output voltage for an inner loop current closed loop, wherein k takes a value of 0.2 in order to enable the injected high-frequency signal to meet the fault positioning requirement and not to influence the fault ride-through function of the IBDG.
And step 205, substituting the N voltage harmonics and the current harmonics on the m side of the protected line with the phase-to-phase fault into a fault loop differential equation, replacing a differential term of the fault loop differential equation with a differential operation, and solving by a least square method to obtain the distance between the fault position and the m side.
It should be noted that, in step 204, two high-frequency harmonics, 400Hz and 500Hz, are respectively injected into the microgrid, so that voltage and current information measured by the m-side protection device of the protected line with a fault of the microgrid is filtered by the band-pass filters with characteristic frequencies of 400Hz and 500Hz respectively, and voltage and current harmonics of the m-side 8 th order and 10 th order are obtained, respectively: u. ofmfh1，imfh1And umfh2，imfh2。
Then, 8 th and 10 th voltage and current harmonics are substituted into a fault loop differential equation, and the differential terms of the fault loop differential equation are:
by means of a difference operation:
instead, the method is similar to the method,
or obtaining the distance L between the unknown number fault position and the m side and the equivalent transition resistance R 'by utilizing a least square method'f。
The following description is respectively given to a typical microgrid system, a fault ride-through control module of a droop control type IBDG, a fault detection module of the droop control type IBDG, an AB phase fault network of a protected line, and a high-frequency harmonic extraction module.
Fig. 4 is a diagram of a typical microgrid system, which includes four busbars, three Inverter-based distributed generators (IBDG), two loads, a protection and monitoring device, and so on. PCC (Point of common coupling) is a public connection point and is connected with a micro-grid and a large-grid, inverters of three inverter type micro-sources IBDG1, IBDG2 and IBDG3 all adopt a droop control strategy, the micro-grid system can be switched between a radiation type network structure and a ring type network structure by controlling the on-off of a ring network switch, and F1, F2 and F3 are fault points on different lines respectively.
FIG. 5 is a fault ride-through control block diagram of the droop control type IBDG, which mainly comprises three parts, namely a power outer loop and a voltage and current inner loop, wherein the control input quantity of the power outer loop is an active reference Po*Reactive reference Qo*Rated voltage amplitude U0Reference angular frequency omega0Voltage sag factor DqAnd frequency droop coefficient DpThe output is a reference voltage UrefAnd a phase θ; the voltage inner loop control input is a reference voltage uod*And uoq*Feedback output voltage uodqFeedforward output current iodqThe output is a reference current ildqr(ii) a The current inner loop control input is a reference current ildq*Feedback of the output current ildqFeedforward output voltageuodqThe output is a dq-axis component u of the modulated wavemddq(ii) a And a coordinate transformation unit for transforming the abc coordinate into the dq coordinate system or the dq coordinate into the abc coordinate system, wherein the input is the reference phase-locked phase theta. The input of the fault detection unit is the output voltage dq axis component u of the inverterodqAnd three-phase output current ioabcThe output is a fault Flag _ f, when the fault detection unit detects that the system has a fault, the switches S1-S3 are all switched to the 1 position, and the current inner loop controls the reference current to be switched to idqsetAnd fault current limiting is realized. In high frequency harmonic fault modules, Umdω and φ1The fundamental wave amplitude, the frequency and the phase of the output voltage at fault time are respectively; k. phi is a unit of8And phi10Respectively a high-frequency harmonic voltage amplitude coefficient, an 8 th harmonic phase and a 10 th harmonic phase.
Fig. 6 is a structural block diagram of a fault detection module of the droop control type IBDG, and the fault detection unit provides conditions for fault ride-through of the three-phase grid-connected inverter by detecting the output voltage state of the inverter in real time and determining whether a fault occurs. The voltage amplitude detection unit and the instantaneous current detection unit are mainly used for outputting a fault Flag _ f by using OR logic. Wherein ioabcFor instantaneous value of inverter output current uodAnd uoqRespectively an inverter output voltage uoabcD-axis component of (I)tripFor a preset value of current, VtripIs a voltage preset value. The voltage amplitude detection unit outputs a voltage amplitude U according to the inverteromAnd is in accordance with the preset voltage value VtripCompared with each other, the instantaneous current detection unit is used for detecting three-phase network inlet current ioabcInstantaneous value and current preset value ItripComparing when U isomLess than VtripOr ioabIs greater than ItripAnd if so, determining that the power grid fails and positioning a fault Flag _ f, otherwise, still keeping the micro-power grid in a normal working condition.
FIG. 7 is a diagram of an AB phase fault network for a line being protected, umabAnd unabLine voltage i between m-side and n-side AB phases of the line to be protectedmaAnd imbRespectively m-side A-phase current and B-phase current of the protected lineCurrent, inaAnd inbRespectively the phase A current and the phase B current at the n side of the protected line, RfTo transition resistance, ifabAnd r and L are resistance and inductance of the line per unit length respectively, L is the distance from the m side of the protected line to the fault point, and D is the total length of the line.
FIG. 8 shows a high frequency harmonic extraction module, umAnd imVoltage and current information, omega, measured by a protective device at the m side of the line to be protectedfh1And ωfh2Two characteristic frequencies of the band-pass filter, 400Hz and 500Hz, umAnd imThe 8 th and 10 th harmonic wave u of voltage and current can be obtained by filtering through a band-pass filtermfh1，imfh1And umfh2，imfh2。
The second embodiment of the method for positioning a single-ended fast fault of a micro-grid provided in the embodiment of the present application is described above, and the following is an embodiment of a device for positioning a single-ended fast fault of a micro-grid provided in the embodiment of the present application.
Referring to fig. 3, an embodiment of a microgrid single-ended fast fault location apparatus provided in an embodiment of the present application includes:
a switching unit 301, configured to switch a droop control mode of the inverter to a current control mode when an output voltage of the inverter of the microgrid is less than a preset voltage or a three-phase grid-incoming current of the inverter is greater than a preset current.
The constructing unit 302 is configured to, when an inter-phase fault occurs between the a phase and the B phase of the microgrid, construct a fault loop differential equation of the m-side a phase and the B phase of the microgrid, and obtain the number N of unknown parameters of the fault loop differential equation, where N is a positive integer.
And the modulation unit 303 is configured to perform inverse park transformation on an inner-loop current closed-loop control output value of the inverter micro source of the microgrid to obtain a three-phase modulation wave, and perform superposition of an X-order harmonic and a Y-order harmonic on the three-phase modulation wave, where X and Y are positive integers.
And the injection unit 304 is configured to inject N high-frequency harmonics with different frequencies into the microgrid according to the number N of unknown parameters, so as to obtain N voltage harmonics and N current harmonics, respectively.
And a calculating unit 305, configured to substitute the N voltage harmonics and current harmonics on the m side of the protected line where the phase-to-phase fault occurs into a fault loop differential equation, and calculate a distance between the fault location and the m side.
According to the micro-grid single-end rapid fault positioning device, whether a micro-grid fails or not is judged according to the output voltage of an inverter of the micro-grid or the three-phase grid-incoming current; when the micro-grid fails, the droop control mode of the inverter is switched to a current control mode, so that fault ride-through is realized; then constructing a fault loop differential equation of the protected line with the fault; then, respectively superposing harmonic waves of different times on modulation waves of inner loop current closed-loop control of the micro-grid inversion type micro-source, and injecting a plurality of high-frequency harmonic waves of different frequencies into the micro-grid, so that the micro-grid filters harmonic voltage and the like of a protected line with a fault through the high-frequency harmonic waves to obtain high-frequency signals; finally, the high controllability of the power electronic converter is fully utilized, fault distance calculation is carried out by adopting high-frequency signals in the power grid, and the fault of the microgrid system can be quickly, accurately and reliably judged and positioned under the condition of no communication, so that the technical problems of low positioning accuracy, long time and unreliability of the conventional microgrid fault positioning technology are solved.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
The terms "first," "second," "third," "fourth," and the like in the description of the present application and in the above-described drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
It should be understood that, in this application, "at least one" means one or more, "a plurality" means two or more. "and/or" for describing an association relationship of associated objects, indicating that there may be three relationships, e.g., "a and/or B" may indicate: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.
In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U-disk, a portable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk.
The above embodiments are only used to illustrate the technical solutions of the present application, and not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.
Claims (9)
1. A method for rapidly positioning a single-end fault of a micro-grid is characterized by comprising the following steps:
s1, when the output voltage of an inverter of the microgrid is smaller than a preset voltage or the three-phase grid-incoming current of the inverter is larger than a preset current, switching the droop control mode of the inverter into a current control mode;
s2, when phase-to-phase faults occur between the phase A and the phase B of the microgrid, constructing fault loop differential equations of the phase A and the phase B at the m side of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer;
s3, performing reverse park transformation on an inner ring current closed-loop control output value of the inverter type micro source of the microgrid to obtain a three-phase modulation wave, and performing superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers;
s4, respectively injecting N high-frequency harmonics with different frequencies into the microgrid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics;
s5, substituting N voltage harmonics and current harmonics of the m side of the protected line with the phase-to-phase fault into the differential equation of the fault loop, and calculating to obtain the distance between the fault position and the m side;
wherein the three-phase modulated wave is:
in the formula umda、umdb、umdcModulated waves, U, of A, B, C phases respectivelymdFundamental wave amplitude of the output voltage for the inner loop current closed-loop control, omega is the frequency of the output voltage for the inner loop current closed-loop control,
and controlling the phase of the output voltage for the inner loop current in a closed loop mode.
2. The method for rapidly locating the single-ended fault of the microgrid according to claim 1, wherein the step S2 specifically comprises:
when an interphase fault occurs between the phase A and the phase B of the microgrid, converting the microgrid into an R-L equivalent model, constructing fault loop differential equations of the phase A and the phase B of the microgrid on the side m according to line voltage between the phase A and the phase B on the side m, phase A current on the side m and phase B current, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein the N is a positive integer.
3. The method for rapidly locating the single-ended fault of the microgrid according to claim 1, wherein the step S5 specifically comprises:
substituting N voltage harmonics and current harmonics of the m side of the protected line with the phase-to-phase fault into a fault circuit differential equation, replacing a differential term of the fault circuit differential equation with differential operation, and solving by a least square method to obtain the distance between a fault position and the m side.
4. The microgrid single-ended fast fault location method according to claim 1, characterized in that the fault loop differential equation is:
in the formula umab(t) is the line voltage between m-side AB phases of the line to be protected, ima、imbRespectively m side A phase current and B phase current of a protected line, r is a resistance per unit length of the line, L is a distance between a fault position and the m side, L is an inductance per unit length of the line, k is a resistance per unit length of the linefAs a branching coefficient into a fault point, RfTransition resistance, R'fEquivalent transition resistance.
5. The utility model provides a quick fault location device of little electric wire netting single-ended which characterized in that includes:
the switching unit is used for switching the droop control mode of the inverter into the current control mode when the output voltage of the inverter of the microgrid is smaller than a preset voltage or the three-phase grid-incoming current of the inverter is larger than a preset current;
the device comprises a construction unit, a fault detection unit and a fault analysis unit, wherein the construction unit is used for constructing fault loop differential equations of an A phase and a B phase at the m side of the microgrid when an interphase fault occurs between the A phase and the B phase of the microgrid, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein N is a positive integer;
the modulation unit is used for carrying out reverse park transformation on an inner ring current closed-loop control output value of an inverter type micro source of the micro grid to obtain a three-phase modulation wave, and carrying out superposition of X-order harmonic and Y-order harmonic on the three-phase modulation wave respectively, wherein X and Y are positive integers;
the injection unit is used for respectively injecting N high-frequency harmonics with different frequencies into the microgrid according to the number N of the unknown parameters to respectively obtain N voltage harmonics and N current harmonics;
the calculation unit is used for substituting N voltage harmonics and current harmonics of the m side of the protected line with the phase-to-phase fault into the fault loop differential equation to calculate the distance between the fault position and the m side;
wherein the three-phase modulated wave is:
in the formula umda、umdb、umdcModulated waves, U, of A, B, C phases respectivelymdFundamental wave amplitude of the output voltage for the inner loop current closed-loop control, omega is the frequency of the output voltage for the inner loop current closed-loop control,
and controlling the phase of the output voltage in a closed loop mode for the inner loop current.
6. The microgrid single-ended fast fault location device according to claim 5, characterized in that the construction unit is specifically configured to:
when an interphase fault occurs between the phase A and the phase B of the microgrid, converting the microgrid into an R-L equivalent model, constructing fault loop differential equations of the phase A and the phase B of the microgrid on the side m according to line voltage between the phase A and the phase B on the side m, phase A current on the side m and phase B current, and acquiring the number N of unknown parameters of the fault loop differential equations, wherein the N is a positive integer.
7. The microgrid single-ended fast fault location device according to claim 5, wherein the computing unit is specifically configured to:
substituting N voltage harmonics and current harmonics of the m side of the protected line with the phase-to-phase fault into a fault circuit differential equation, replacing a differential term of the fault circuit differential equation with differential operation, and solving by a least square method to obtain the distance between a fault position and the m side.
8. A microgrid single-ended fast fault location device, characterized in that the device comprises a processor and a memory:
the memory is used for storing program codes and transmitting the program codes to the processor;
the processor is used for executing the microgrid single-ended rapid fault location method according to any one of claims 1 to 4 according to instructions in the program code.
9. A computer-readable storage medium, characterized in that the computer-readable storage medium is configured to store program code for performing the method for single-ended fast fault location of a microgrid according to any of claims 1 to 4.
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| CN115377952B (en) * | 2022-10-19 | 2023-03-24 | 温州电力建设有限公司 | Active detection type protection method for phase-to-phase fault of distributed photovoltaic grid-connected line |
| CN116054106B (en) * | 2023-03-15 | 2023-06-30 | 国网浙江省电力有限公司 | Low-voltage distribution network cooperative anti-islanding protection system, method and related equipment |
| CN116754899B (en) * | 2023-08-21 | 2023-10-17 | 深圳市德兰明海新能源股份有限公司 | Grid fault detection method and device for micro-grid-connected system |
| CN118655421A (en) * | 2024-08-20 | 2024-09-17 | 兰州朗青交通科技有限公司 | Fault positioning method of expressway micro-grid system |
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